1. Field of the Invention
The present invention relates to a detergent composition for cleaning a precision part. More specifically, the present invention relates to a water-containing detergent composition for cleaning a precision part such as a metal part, an electronic part, a semiconductor part or a liquid crystal display panel.
2. Discussion of the Related Art
Conventionally, wire connections of a printing substrate, a semiconductor package or the like have been carried out by solder connection via screen printing using cream solder. This cream solder comprises a eutectic solder component containing tin/lead, and a so-called flux component containing a resin, an active agent, an antioxidant, a thixotropic agent, and a solvent, which is used for the purposes of increasing screen printability and wiring reliability after connection. The flux component included herein has an important function of removing a metal oxide coating film at the connecting portion and the like. However, once the connection is completed, the flux component has a possibility that the reliability of the part is lowered thereafter, such as hygroscopicity, so that the flux component must be completely removed by cleaning the part.
In the removal of this flux component, a fluorocarbon-based solvent and a chlorine-based solvent have been used up until the 1990's in order to utilize its characteristics such as high detergency and fire retardancy. However, the detergent using a chlorine-based solvent or a fluorocarbon-based solvent has serious problems in safety, toxicity, environmental pollutions, and the like, so that these solvents were totally banned. Therefore, as a process to be used in place of these solvents, there have been numerously marketed a so-called water-containing flux detergent which takes into consideration of a risk such as ignition property by solubilizing water in a non-water-soluble component such as an organic solvent.
Recently, however, from the viewpoints of the development of finer wiring pitches and environmental protection needs, a composition of the flux has been modified in order to meet these needs in the cream solder component. Concretely, in order to increase the viscosity of the cream solder, the amount of the thixotropic agent in the composition of the flux tends to be increased. The reasons why the viscosity is to be increased are such that printing reliability in finer screen printing is improved and that edge rounding upon heating due to the modification of the non-lead-containing solder metal which has a higher melting point is prevented.
On the other hand, this flux component showing low solubility has been known to have high solubility to benzyl alcohol. Therefore, there has been disclosed a flux detergent using benzyl alcohol as a dissolution aid. For instance, Japanese Patent Gazette No. 2041987 discloses a non-water-based detergent composition comprising benzyl alcohol (or 2-phenetyl alcohol) as a main component, and a nonionic surfactant being added thereto; Japanese Patent Laid-Open No. Hei 4-34000 discloses a non-water-based detergent composition comprising benzyl alcohol as a main component; Japanese Patent Laid-Open Nos. Hei 6-346094 and Hei 9-255995 each discloses a water-containing detergent composition comprising 3-methoxy-3-methylbutanol as a main component, and benzyl alcohol and water being added thereto; Japanese Patent Laid-Open No. 2000-8080 discloses a water-containing detergent composition comprising benzyl alcohol as a main component, and a water-soluble glycol ether, a nonionic surfactant and water being added thereto. Also, as the detergent containing a glyceryl ether, Japanese Patent Laid-Open No. Hei 6-346092 discloses a detergent composition containing a glyceryl ether having a hydrocarbon group having 1 to 18 carbon atoms. Among them, the present inventors have carried out a cleaning test for a so-called water-containing flux detergent which has taken into consideration a risk such as ignition property. As a result, although the detergent shows high flux detergency against a generally used eutectic solder containing tin/lead, the detergent shows unsatisfactory detergency to flux in a lead-free solder or a solder for fine pitches in which the amount of the thixotropic agent such as N,N-ethylenebisstearamide is increased. Also, the detergent using a glyceryl ether as a dissolution aid also has unsatisfactory detergency to flux in a lead-free solder or the like as mentioned above.
In addition, as to the removal of the liquid crystal stains, the gap distance between the liquid crystal cells becomes even narrower with the development of thinner liquid crystal display panel, so that it has been becoming increasingly difficult to clean the liquid crystals existing in the gap. When the conventional detergent composition as mentioned above is used against the liquid crystal stains, the detergency is unsatisfactory for those liquid crystals existing in the gap, even though the detergency is excellent for the liquid crystals existing on the surface.
An object of the present invention is to provide a water-containing detergent composition for cleaning a precision part, which shows high detergency to flux when a lead-free solder and a solder for fine pitches is used as a solder in addition to the eutectic solder, and shows high detergency against stains mainly composed of organic substances existing on the surface of a metal part, an electronic part or a semiconductor part, or liquid crystal stains in a liquid crystal display panel, and the detergent composition having excellent safety.
These and other objects of the present invention will be apparent from the following description.